Izumi Norimoto is a high school student distinguished by his black hair and brown eyes. He lives next door to Kazusa Onodera, sharing a childhood friendship that began in their early youth. This bond initially resembled a sibling-like connection but grew strained during middle school when Kazusa developed romantic feelings for him. Peer pressure further complicated matters, leading Kazusa to distance herself upon entering high school.

Characterized by kindness and caring, Izumi remains inexperienced in love and sexuality. His struggle to differentiate romantic attachment from physical attraction becomes a significant source of conflict. After Kazusa joins the literature club and catches him in a private moment, he becomes aware of her feelings. He eventually confesses his own romantic feelings for her, and they begin a relationship. However, he simultaneously experiences intense sexual attraction to Niina Sugawara, Kazusa's best friend, who actively pursues him despite his commitment to Kazusa. This creates a volatile love triangle where Izumi openly admits his physical desire for Niina while asserting his emotional commitment to Kazusa, causing emotional turmoil for both girls.

Niina Sugawara's manipulations, such as engineering situations to initiate physical contact, intensify the tension. Izumi's internal conflict culminates when he candidly acknowledges his dual feelings: romantic love for Kazusa and sexual desire for Niina. This honesty fractures his relationship with Kazusa but forces him to confront his emotional immaturity. His journey involves navigating guilt and the fallout of his actions, ultimately leading him to recommit to repairing his bond with Kazusa, prioritizing emotional connection over physical impulses.

His background lacks detailed family history or broader life events beyond his relationships with Kazusa and the literature club. His surname, Norimoto (典元), combines characters meaning "rule, ceremony" and "beginning, origin." His given name, Izumi (泉), means "fountain, spring."